Split-and-mix synthesis approaches have been used to produce peptide libraries on small beads, with each bead containing an individual peptide molecule. Such libraries are referred to as one-bead-one-compound (OBOC) libraries. A common use of OBOC libraries is to identify molecules from the libraries that perform some function of interest. As an example, an OBOC library may be used to identify a molecule (i.e., a peptide) that binds to a particular protein by screening the library for beads that are associated with the protein (“hit” beads). The hit beads can be separated from the rest of the library, and the identity of the peptide on a particular hit bead can be determined using a peptide sequencing strategy.
Peptide sequencing using mass spectrometry is complicated by the existence of amino acids with similar masses (e.g., isobaric amino acids) that cannot be differentiated by mass spectrometry. Thus, a need exists for methods for differentiating isobaric amino acids.